Too cool for comfort

Everyone loves the cool breeze of air-conditioners (ACs). But at what temperature are we really comfortable? Is it 18°C? In that case are we cooling ourselves or refrigerating our bodies? The National Building Code puts the desirable indoor temperature during summers at 27.5°C. What if we keep the thermostat at 27°C for this summer? Use this calculator to find out how much money you are wasting by not doing so?

Last Updated: Wednesday 15 July 2015

Too cool for comfort
Everyone loves the cool breeze of air-conditioners (ACs). But at what temperature are we really comfortable? Is it 18°C? In that case are we cooling ourselves or refrigerating our bodies? The National Building Code puts the desirable indoor temperature during summers at 27.5°C. What if we keep the thermostat at 27°C for this summer? Use this calculator to find out how much money you are wasting by not doing so
The calculation result is the money in Indian rupee you would have saved had you used your AC at 27 degree Celsius. National Building Code puts the optimum temperature condition at 27.5 degree Celsius. Also, ACs rated efficiency is tested at 27 degree Celsius.




  1. Star ratings are in accordance with the Bureau of Energy Efficiency's Energy Efficiency Guide: Buying and Maintaining an Energy-Efficient Room Air Conditioner
  2. The calculator is applicable to window and split AC only. The calculation is based on a single AC's usage of eight hours a day, 30 days a month.
  3. The calculator compares saving amongst same star-rated ACs at different temperature settings; it doesn't compare performance of different star-rated ACs.
  4. Calculation Logic -- Your AC performs at star rated capacity only if it's set at 27 degree Celsius. Different studies suggest your AC's efficiency could drop by 3% to 10% with every degree lower than this. We have taken a mean 5% drop for every degree below 27 degree Celsius, which is also in line with assumptions by Delhi's power supplier, Tata Power Delhi Distribution Limited. We have multiplied this calculation by your city's tariff and your monthly usage.
  5. The monthly money wasted is an indicative value, there are other factors which can also influence your ACs efficiency.
Air Conditioners (AC) tip sheet
A properly designed building won’t require you to be dependent upon AC for your thermal comfort. Unfortunately, most of us are not so lucky. We live in houses and apartment buildings that can’t be shifted around on site or significantly renovated. With that in mind, the most obvious place to look for improving your home’s energy efficiency is the mechanical systems that provide heating and cooling. If you really need to have one, here are some tips apart from setting your thermostat at 27°C to limit the energy needs of your air conditioner and increase its cooling power.

    1. Choose what to cool
      Best practice is to select rooms or spaces in your house that you would like to air condition, as you don’t need to air condition whole of your house. Spaces like kitchen, corridors, foyers and bathroom don’t need any air conditioning as you hardly spend any time there. Conditioning them won’t only be wastage of money but valuable resources of earth.
    2. Fix your room
      Once you have decided which spaces to condition, try insulate and airtight these spaces. Close the windows and doors draw blinds and curtains. You don’t want outside heat to seep into your room via walls and windows, or the hot exterior air to mix with your cooled interior air.
    3. Stars to rescue
      When purchasing an air conditioner check its star rating. The Energy Rating scheme rates the energy efficiency of electrical products and appliances to help you with your purchasing choices. When comparing different appliances or equipment it is important to look at comparative energy consumption, which is shown in kilowatt-hours, rather than just the number of stars.
    4. Size it right
      Size your AC according to your need, an AC that is too big is inefficient and wastes money. Ideally you want your AC to run at least ten minutes before it kicks in. Oversized AC’s cool the house down too quickly and then cut off before they've reached their most efficient running level. A properly-sized system that runs longer saves money over an oversized system that runs for shorter periods of time.
    5. Don’t over run
      It’s a myth that it takes less energy to run the AC all day, rather than leaving it off and turning it on when you get home. Running the AC all day when you're away definitely uses more energy, no question. The reason is that with the AC constantly running, it’s constantly cooling your home, making it a heat magnet. Heat goes to where it’s not, so when your house is cooler, more heat will try to enter. So more heat gets into your house, and the AC has to remove that heat, over and over again. But if you leave the AC off, then the house will heat up during the day and then stop heating up. It’s already hot so it’s no longer a heat magnet. When you get home and turn on the AC, it has less total heat to remove than if it had been running all day.
    6. Shade your AC
      Shade your condensers. A well shaded condenser will use up to 10% less electricity than those in direct sunlight. Remove tall grass and other debris on or around the condenser as they can restrict air flow and increase electricity consumption.
    7. Fan it down
      We are most comfortable in a temperature range of 24-28 degree centigrade, so keep your AC thermostat at these levels. In fact every degree below 26 on the thermostat increases the energy consumption of AC. If you prefer lower temperature it would be wiser to club your AC with a ceiling fan. A ceiling fan can effectively bring down temperature by 2-4 degree centigrade, at much lesser consumption of energy. A fan will cost maximum one rupee an hour to bring down same degree of temperature which an AC will do consuming 10-15 rupees an hour
    8. Clean the filter
      Clean the filter of your AC regularly as it can help reduce the energy consumption by almost 10 per cent. A clean filter means lesser energy to pump air through them.
The bush shirt rule(s)
Author: Sakshi Chadha Dasgupta


Waning winter is the time when people call up their dry cleaners to get heavy business suits and jackets cleaned before packing them for the next season. Soon the wardrobes are occupied by bush-shirts, kurtas and T-shirts made of cotton and linen, which are perfect to keep people cool through heat and sweat.

But air conditioning is probably changing the way we dress. Conference rooms, auditoriums, workspaces and malls are running their air conditioners at as low as 18-19°C to keep it cold for their employees and visitors. The question then is: Is cold is really comfortable?

At such low temperatures, only a person wearing a climate-inappropriate three three-piece business suit or a stretch lycra jeans would feel fine while someone who is clad in a summer-friendly bush-shirt would be quivering in the cold. Besides being too cool for comfort, there are monetary implications of keeping the ACs at such low temperatures. For every degree decrease in thermostat setting, there is increased energy consumption of fiveper cent. So there would be fatter bills to pay to keep temperatures low.

It is surprising that India with all its energy concerns never gave serious consideration to appropriate clothing as an energy conservation measure. Our neighbour, Pakistan, has proved to be the smarter one. Like in most parts of India, temperatures in some parts of Pakistan reach around 40°C in peak summers. The Pakistani PM’s office has prescribed a dress code for summers. The dress code recommends light-coloured, loose-fitting clothes to combat summer heat. Government employees will also be allowed to wear shoes without laces or sandals without socks at work. Further, the government has also gone ahead with stricter steps–like banning air-conditioners in its offices–to cope with power shortage. The Japanese have also mandated season appropriate dressing for building occupants. So three piece suits are out for them in peak summers, and peak summer for them is just around 30°C!

So isn't it time Indians start to dress down and flaunt the cool bush–shirt. Wear light to set things right. Right?

Too cool for comfort


Author(s): Sakshi Chadha Dasgupta, Disha Singh
Issue Date: May 15, 2013

How rising incomes are lowering room temperatures at the cost of energy, health and comfort

“I can’t imagine my day without air-conditioners. I even ensure that I buy vegetables and fruits from an air-conditioned supermarket,” says 28-year-old Deepali Sinha Kapoor, a marketing executive in an IT firm in Lucknow. Kapoor is so used to cool spaces that besides spending long hours in her air-conditioned office, she spends her weekends touring air-conditioned malls.

Like Kapoor, many young people and families crowd malls and multiplexes in the summer to escape the heat and revel in crisp air-conditioned comfort. Manufacturers, cashing in on the summer frenzy for air-conditioners (ACs), dole out attractive offers. Originally, it were manufacturers of products susceptible to heat and humidity, like tobacco, chocolate and colour printing, who had commissioned experiments in mechanical cooling. Emphasis has shifted to comfort systems, with air-conditioning aimed more at cooling living space than equipment and consumer items.

Higher disposable incomes and accompanying lifestyle modifications are major drivers of the demand for ACs in India. “People want to feel comfortable both at home and at their workplaces and ACs provide them this comfort,” says Anup Bhargav, senior general manager, Godrej Appliances.

A study by Mckinsey Global Institute (MGI) states the middle class in India will swell from 50 million at present to about 583 million by 2025. That will be 41 per cent of the population. This upwardly mobile middle class is likely to use ACs, vacation annually, dine out and opt for global brands, according to MGI. Small wonder then the AC market in India is growing at over 30 per cent annually.

Rising expectations

Studies show that living and working in buildings with strictly controlled temperature conditions raises thermal comfort expectations. People become accustomed to air-conditioning and do not want to settle for anything less. India is beginning to show signs of this discomfiting trend.

“Overindulgence in air-conditioning has made people its captive users and they hardly venture outdoors,” says S K Chhabra, head of cardio-respiratory physiology, Vallabhbhai Patel Chest Institute in Delhi. “A large number of parents that come to us for admission enquire about air-conditioned classes. Today it is a matter of competition and fully air-conditioned schools score over others,” says Richa Khandelwal, a counsellor at Euro Kids, India’s largest preschool chain.

good living

Some architects believe that Indians need to use ACs only during the peak summer months. A well ventilated room with a fan at maximum speed can provide adequate comfort the rest of the year. The demands of modern living have substituted traditional commonsensical measures, such as wearing light clothing, eating light and taking afternoon siestas, with more energy-intensive cooling mechanisms.

“Medical science has established that being exposed to a wide temperature range allows the body to be more resilient in the face of variation. Instead, most people today prefer to have an artificially controlled environment through mechanical cooling,” says architect Gaurav Shorey. “What’s even worse is that people wear three-piece business suits or stretch jeans and then run ACs at 19°C to keep themselves cool. What is it that stops them from wearing a cotton shirt or a kurta which can keep the body cool naturally,” asks Shorey.

Inconsistent norms

Building norms do not sufficiently address thermal comfort. The National Building Code of India (NBC) 2005 describes human thermal comfort as a condition of surrounding thermal environment under which a person can maintain a body heat balance at normal body temperature without perceptible sweating. It depends on factors like age, metabolic rate and clothing, which in turn are affected by air temperature, relative humidity, radiation from solid surroundings and rate of air movement.

The tropical summer index (TSI) is a tool that helps determine the combination of variables such as temperature, relative humidity and air velocity that makes a person feel comfortable. NBC states that the thermal comfort of a person lies between TSI temperature values of 25°C and 30°C with optimum condition at 27.5°C. But for air-conditioned spaces the same code proposes an indoor temperature range of 23-26°C for summers and 21-23°C for winters.

The Bureau of Energy Efficiency’s Energy Conservation Building Code (ECBC), which aims to regulate energy consumption of commercial buildings that usually have ACs, does not define temperature and humidity standards. “Ideally, codes should specify the range of temperature conditions specific to the climate,” says Rajan Rawal, coordinator, Centre for Advanced Research in Building Science and Energy at CEPT University in Ahmedabad. In one of his studies Rawal highlights that without thermal comfort standards customised for Indian climatic conditions, air-conditioned office buildings in India operate at 22.5 (± 1°C). Consequently, mechanical systems have to use massive energy to cool temperatures down from 42-45°C to 21-22°C.

Health effects

“Well conditioned spaces encourage people to work longer and more productively,” says Bhargav. However, a 2004 Cornell University study highlights that uneven airflow in cooled buildings often leaves some people shivering and others sweating in corners, thus affecting their performance at the workplace.

“For almost three months all I did was sneeze and cough throughout the day,” smirks Zubaan Syed, an aspiring architect. “After living in Puducherry for a year without any ACs my body got rude shocks everywhere in Delhi where ACs were always on. Doctors made me undergo all kinds of expensive tests and prescribed a host of medicines, but nothing seemed to be working,” he adds.

The Indian AC market, however, seems to be in good health. According to a study by the Associated Chambers of Commerce and Industry of India, the room AC market in India was estimated at 4.2 million units in 2011 and was valued at Rs 7,200 crore. The demand for ACs is shifting from big metropolitan cities to medium and small cities. “The residential segment is growing rapidly at the rate of 8-9 per cent, with greater demand for spilt ACs,” says Bhargav. A growing number of Indian and international studies highlight the perils of excessive air-conditioning on human health. Chhabra cautions that a sedentary air-conditioned lifestyle could cause obesity, cardiovascular diseases and psychological infirmities. A preliminary study done by a team of doctors from various medical colleges in India found the frequency of respiratory symptoms like coughing, wheezing and breathlessness was higher among AC users.

“Now that summer is back with ACs roaring on maximum, I am afraid that my problems may reappear,” says Syed. “Maybe this time I will carry a jacket and a cap around.”


Subscribe to Weekly Newsletter :

Comments are moderated and will be published only after the site moderator’s approval. Please use a genuine email ID and provide your name. Selected comments may also be used in the ‘Letters’ section of the Down To Earth print edition.

  • Excellent information.

    Excellent information. Everybody should read.
    Dr.A.Jagadeesh Nellore(AP),India

    Posted by: Anonymous | 7 years ago | Reply
  • This is a good initiative but

    This is a good initiative but this shows that the difference in wastage between a 5 star rated AC and a 1 star rated AC is not even 400/month. Please try to present it in a better way such that the benefits are more evident..may be u can show total difference for 3 summer months in delhi

    Posted by: Anonymous | 7 years ago | Reply
  • Frankly speaking, I have

    Frankly speaking, I have never seen any ac operating at 27 degree, which is the basis of your calculation.

    Secondly, I feel sad after doing all the calculations. I have purchased 5 start ac and your calculations says that at 22 degree, I am able to save only Rs 200 per month with respect to 1 start ac.

    Posted by: Anonymous | 7 years ago | Reply
  • Jai hari Krisna. Very good

    Jai hari Krisna.
    Very good initative & the good tips.
    Use of the fan Fan & A.C. simultaneously is a very useful suggestion.

    For a 1,200 Sq feet one plus one bungalow in the
    8 rooms 0.75 Tone 4 * A.C."s in each room are installed & used for the 12 hrs a day.
    If insted of the A.C. on 2 H.P.Pumpset from the outside
    70 fooggers are installed with 0.5 litre discharge per hr.
    with the timer & used for 6 hrs a day.
    Usingthe rain water harvested & recycled water.
    Maintaing the temperature around 20 degree.
    The capital cost for installing the fogger systeme including pupsate,piping,installing is 30 % than installing the A.C.

    Which will be more energy saver / how it can be calculated & compared?

    Thank You
    Raju Gandhi
    The Promoter Of The wealth Creation Concept Of
    Sheti Udyog Bhandar
    Swargate Pune 0 98220 52586

    Posted by: Anonymous | 7 years ago | Reply
  • I have been using the AC only

    I have been using the AC only at 27 as at one point time I realized that below that temperature we require a blanket after sometime. But I recently read in book (with no reasoning) that when the thermostat is set above 23 (i.e. 24,25..) then the AC bursts as we hear now and then about AC accidents. Is it true?

    Posted by: Anonymous | 7 years ago | Reply
  • Excellent initiative but you

    Excellent initiative but you should have consulted someone who has an in-depth knowledge of the subject. It is not possible to check the validity of the calculation as it is like a "black box". But the accompanying text is atrocious. How do you explain a sentence like: "your AC performs at star rated capacity only if it is set at 27 deg.C"? Efficiency is simply defined as "output / input". What has that got to do with thermostat setting. Just imagine someone saying: "your water pump will work at the best efficiency if you set the automatic cut-off level in the tank at the mid-level". A thermostat just does what it is supposed to do: cut-off the compressor when the set temperature is reached. If you set the temperature higher, the room temperature will be achieved faster, hence the compressor will cut off and you can save electricity. It has nothing to do with the AC performing at star rated capacity.
    You seem to say the only parameter that determines comfort is the ambient temperature! What about the humidity, air velocity, temperature of surrounding walls, ceiling and objects. Try making yourself comfortable at 27 deg.C in a poorly designed room where the sunlight is falling straight on your wall which is fully glazed (that is unfortunately how our modern buildings are designed: solar ovens being refrigerated with the help of air conditioner).
    And where did you get the idea that a ceiling fan can "effectively bring down the temperature by 2 to 4 deg.C"? The fan does exactly what it is supposed to do: move the air. When the air comes into contact with your body, it carries away the sweat from your body, thus helping to get rid of your body heat and cooling you. But when you are in a very humid environment, the fan cannot do much to evaporate the sweat. In fact when a fan runs, the electricity it needs adds heat into the room. So it is wiser to switch off the fan if there is nobody in the room.
    Where did you get this idea that "a fan will cost maximum one rupee an hour to bring down the same degree of temperature which an AC will do consuming 10-15 rupees an hour". I have already explained what exactly a fan does. Do you know how much electricity does a fan consume? A 5-star fans needs 50 W and will consume 0.05 kWh (units) if it runs an hour. If you take the highest electricity rate (7.75 rupees in Kolkata), running the fan will cost less than 0.4 rupees per hour.
    Sorry for being so long but I hope I have made my point. It is very good that you want to educate people but do take the help of someone who knows the subject in order to avoid misguiding people.

    Posted by: Anonymous | 7 years ago | Reply
  • Res Sir, Great information.

    Res Sir,

    Great information. Thanks for your awareness.

    With love,


    Posted by: Anonymous | 7 years ago | Reply
  • Tip of the day on saving

    Tip of the day on saving power.

    Use AC at 26 Degree centigrade with the fan at speed 2. The same cool effect with power saving too.


    Posted by: Anonymous | 7 years ago | Reply
  • Dear Anonymous reader,

    Dear Anonymous reader,

    Highly appreciate your frankness and keen observation. Yes we hardly see any AC operating at 27 degree, even though the standard testing conditions set to determine their efficiency is set at 27 degree according Bureau of Indian Standards and International Standards Organization. Which means that the efficiency mentioned on the AC unit holds only if it is set to cool the interiors down to 27 degree. Point here is if the efficiency is rated for cooling down to 27 degree and our natural comfort lies in between 25-30 degree, then why are the ACs running at 16-18 degree. It is blatant waste of energy and resource, and an end user should be aware of it. Ultimate choice to run the AC rests in the end-user, and this tool is just for awareness so that an informed choice could be made.

    Your second observation is interesting, let me explain. The calculator only compares saving of the same star rated ACs at different temperature settings. It is erroneous in this case to use it to compare performance of different star rated ACs. By deducting the result displayed for a 1 star AC from that of the 5 star AC (at the same temperature), the value arrived is not indicative of the absolute savings as it may seem. Taking this difference value as the savings that would incur from installing a 5 star Ac instead of a 1 star is not correct, as calculator gives results in form of difference between base-case and your chosen case, not absolute consumption numbers which can be compared. Result of 200 in your particular case is the difference in money wasted factoring drop in efficiency, your actual saving may be higher than 200 if the comparison is drawn for same temperature setting. In short, you should not use this calculator to compare different star rated ACs.

    Hope this clears all doubts.


    Posted by: Avikal Somvanshi | 4 years ago | Reply
  • Dear Raghavan, The standard

    Dear Raghavan,

    The standard testing conditions set to determine their efficiency is set at 27 degree according Bureau of Indian Standards and International Standards Organization. Which means that the efficiency mentioned on the AC holds only if it is set to cool the interiors down to 27 degree. Anything below 27 degree reduces its efficiency. So ACs are designed to work at 27 degree, and if they are exploding at setting above 23 degree then there is some serious flaw with the unit and you should contact the manufacturers and demand a replacement and may be compensation too. Personally I have not heard of ACs exploding.

    Thank you.


    Posted by: Avikal Somvanshi | 4 years ago | Reply
  • Really a great tips for Air

    Really a great tips for Air Con users. Normally in winter we never use AC when outside temperature is raised to 28 degree Celsius, and Thus for a comfort, as recommended, 27 degree Celsius is right setting. We do use our 5 * AC whole night and always comfortable and sometimes need thin spread sheet to cover.

    Use of fan suggested is a very good tip. Give some more tips on whether the fan should keep running through out the use of AC, as the service man from AC company keep saying that do not use the fan while AC is on.

    With Best Regards

    Hiten Shah.

    Posted by: Anonymous | 7 years ago | Reply
  • Dear Avikal, Please refer to

    Dear Avikal,
    Please refer to my earlier comment regarding the air conditioner efficiency. You seem to insist on the fact that the air conditioner efficiency will reduce if the room temperature is set lower than 27 deg.C. The BIS or ISO test conditions always refer to both indoor and outdoor temperatures. The air conditioner performance given by the manufacturer corresponds to this "standard condition". Its power consumption will depend on both the inside and outside temperature, which means if the outdoor temperature is higher or lower than the standard condition, the AC will consume more or less power. It does not in any way increase or decrease the AC efficiency. Efficiency is decided mainly by the way the machine is designed: performance of compressor, heat exchanger material and area of the condenser and evaporator, etc. The actual power consumption will depend on the difference between indoor and outdoor air temperature. Please consult any ASHRAE or ISHRAE expert who can explain this to you.

    Posted by: Anonymous | 7 years ago | Reply
  • No doubt this is very good

    No doubt this is very good initiative and scientifically and logically speaking correct way of informing. However, I'm critical of scope of DTE reason it mentions only symptoms in the system not complete overhaul. You may justify that it primarily it focuses on Science and Technology not policy and governance issue but I think time has come to completely eliminate the disease. Here, you mentions only power wastage and appeal to economic logic of end-user what missing criticism of Govt. for failure to implement the rules. I've filmed my neighbor wasting precious fresh water to clean car just because they are rich they can have their way in Socialist country like India (sarcasm to preamble of India Constitution)

    Posted by: Anonymous | 7 years ago | Reply
  • Dear Brahmanand, Wonderful

    Dear Brahmanand,

    Wonderful analysis of our calculator and I highly regret that you found our accompanying text ÔÇ£atrocious.ÔÇØ IÔÇÖm highly appreciative of your enthusiasm and knowledge you have shared with us at Down To Earth. Your observations and insight are welcomed but it is the interpretation of the information I would like to clarify.

    Let me start with, ÔÇ£How do you explain a sentence like: 'your AC performs at star rated capacity only if it is set at 27 deg.C'? Efficiency is simply defined as "output / input". What has that got to do with thermostat setting.ÔÇØ Well, efficiency of all the appliances are tested at very sterile set of test conditions defined by International Standard Organization (ISO) or Bureau of Indian Standards (BIS) or similar body recognized by the country concerned. BIS which is the nodal body in India, defines one of the test standard test condition for AC as cooling down an exterior temperature of 35 degree centigrade to 27 degree centigrade. Other conditions induce space size, humidity levels and more. Energy Efficiency Ratio (EER) which is used to determine the star ratings is the ratio of cooling in British thermal unit (BTU) to the energy consumed in watt-hours (Wh). A Btu is the amount of heat necessary to raise the temperature of 1 pound (0.45 kilograms) of water one degree Fahrenheit (0.56 degrees Celsius). In India we normally convert BTU to Wh, and get EER as a pure number. 1 BTU = 0.29 Wh. Thus you see temperature or thermostat setting is very critical to ACÔÇÖs efficiency. Therefore when the packaging of AC reads ÔÇÿ3.0 EERÔÇÖ it means that the AC will cool down one ton (or the capacity it is designed for) volume from 35 degree centigrade to 27 degree centigrade using one third the amount of energy. And if you ask the said AC to do something other than that it will perform differently. To put it in less technical term, it is same as mileage of a car. ÔÇÿCar will give you 30 km per liter of fuel if you run it at 55 km/hr, on a perfectly horizontal and friction less roadÔÇÖ.

    We never said ÔÇ£the only parameter that determines comfort is the ambient temperature!ÔÇØ. We never even implied that it is the only parameter which determines the ACÔÇÖs efficiency either. In fact the point number 5 of our list of assumption on home page reads, ÔÇ£The monthly money wasted is an indicative value, there are other factors which can also influence your ACs efficiency.ÔÇØ And in our tip-sheet ÔÇ£increase your ACÔÇÖs efficiencyÔÇØ, we have give wide range of fixes which deal with insulation and air leakages in the conditioned space. Kindly take note.

    Furthermore, I totally agree with your observation that ÔÇ£our modern buildings are designed: solar ovens being refrigerated with the help of air conditionerÔÇØ. We have serious objection to glass-houses being constructed in India, and we are vocal about this illogical trend ( But we cannot ask people to break down the walls and roofs of the houses they live in, in todayÔÇÖs urban India majority doesnÔÇÖt get that option. Therefore we are suggesting people to do what they can do on a personal level to help reduce the energy burden.

    I must thank you for beautifully describing how a fan works and cools our body. And when I recommended using a fan to bring down the temperature further by 2-4 degrees, we recommend so in combination with AC. And it is the perceived temperature change, which many top architects around India also second. One will feel cooler at same ambient temperature if the fan is running than other way round. AC usually controls the humidity in the conditioned space irrespective of thermostat setting, thus if one is not comfortable at 27 degree turning on the fan will make a drastic impact. And as your calculation showed running a five star fan ÔÇ£will cost less than 0.4 rupees per hourÔÇØ in Kolkata. Compare that with lowering 4 degree on the five star AC will cost you 2.65 rupees per hour (according to this calculator). Now take the case if its 31 degree outside using fan will still cost 0.4 but using AC will cost more than 13 rupees an hour. I don't quite understand your objection here to "that 'a fan will cost maximum one rupee an hour to bring down the same degree of temperature which an AC will do consuming 10-15 rupees an hour."

    In a hot and humid climate, cross ventilation is the best way to cool off as per all design norms and architects. I find it difficult to believe when you say ÔÇ£in a very humid environment, the fan cannot do much to evaporate the sweatÔÇØ, personally having lived in Pondicherry for a year I can say with certainty that a simple fan worked for wondrously.

    Lastly, I overwhelmingly agree with your point that ÔÇ£it is wiser to switch off the fan if there is nobody in the roomÔÇØ, in fact one should switch off all the appliances not just fans in the room if nobody is there.

    Let common sense prevail.

    Very best,

    Posted by: Avikal Somvanshi | 4 years ago | Reply
  • Dear Brahmanad, Thank you

    Dear Brahmanad,

    Thank you again for enriching our knowledge base. Kindly refer to my reply to your original comment, as logic to most of your reservations I've cleared there. Further, I am fully aware that the performance of the AC will be dependent upon both external and internal temperature conditions, and I agree with your explanation that " power consumption will depend on both the inside and outside temperature, which means if the outdoor temperature is higher or lower than the standard condition, the AC will consume more or less power". Unfortunately, one has no control over the external temperature condition, but the internal temperature can be set, that is what this calculator is requesting people to do.


    Posted by: Avikal Somvanshi | 4 years ago | Reply
  • Dear Sudhir, You have raised

    Dear Sudhir,

    You have raised a very valid issue of government lapse in implementing and monitoring policies and rules. We at Centre for Science and Environment are committed to the cause and have been actively advocating for better policies and governance, via direct involvement with governments/authorities and writing in Down To Earth.

    We believe initiation needs to start both at government level and end-user level, and this calculator is part of our engagement with the end-user, in the way which is easily digestible by them (economics). I personally agree with you that the problem of resource abuse runs way deeper and requires radical measures. But our experience has taught us that radical doesn't go down very well with the society. Something radical like outlawing AC like Pakistan did recently to curb energy crisis only leaves bad taste and resentment among people.

    Lets face it we no longer live in our gorgeously designed traditional houses which did not need artificial cooling. Today in our match box buildings which are designed defying logic, one needs an AC to keep his/her cool. But yes there is a way to use it to and that what we aim to highlight here.
    Rest assured we are waging a war against the mindless construction which is making India captive user of resource intensive technologies like ACs among others. We have already raised voice against glass houses cropping up in our cities, and you will be reading more from us on this in near future.

    Thank you.


    Posted by: Avikal Somvanshi | 4 years ago | Reply
  • Dear Hiten, Nice to hear you

    Dear Hiten,

    Nice to hear you run your AC at 27. Using fan to compliment AC and the extent of it, is subjective to your personal comfort needs. I suggest you should experiment a little bit with various combinations. In our office, we run the AC at highest temperature setting and then adjust fan speed as per our personal comfort. Normally fans run at full speed at afternoon when the sun is beating down on our wall, and at lower speeds in morning and evening. Sometimes we even switch of the AC and keep only the fan, all dependent on the weather outside.


    Posted by: Avikal Somvanshi | 4 years ago | Reply
  • Dear Avikal, Thank you for

    Dear Avikal,
    Thank you for responding point by point to my comments. May be I was a bit too harsh in my judgement considering the fact that DTE is doing a great job in raising issues and sensitizing people. Thanks to the references provided by you, I enjoyed going through the very interesting articles published by Sunita, Disha and Sakshi related to the so-called "green buildings".
    I accept most of your explanations to my comments. However, your analogy of the milage of the car does not hold true for the air conditioner. Please refer to my analogy of the water pump trying to fill in a tank with a level controller. The performance of the AC depends on the condensing and evaporating temperature of the refrigerant inside the machine. The outdoor conditions determine the condensing temperature but the indoor conditions do not determine the evaporating temperature which is dependent on the setting of the expansion valve. In fact, the evaporator functions at a much lower temperature than the room temperature as it plays an important role of cooling the small amount of air (that passes through the cooling coil) to a temperature below its dew point, hence removing the moisture from the air and lowering the indoor air humidity. This is crucial in hot and humid climates because much of energy of the air conditioner goes to remove the humidity from the conditioned air. The AC efficiency is not affected by the set room temperature. The role of thermostat is to cut off the compressor when the set temperature is achieved. So when one sets the thermostat at a higher temperature level, the compressor cuts off earlier whereas when the thermostat is set at a lower temperature, then the compressor has to work for longer time. So the correct analogy would be: if you reduce the distance travelled, the car will consume less fuel.
    I am pleased to learn that you have spent one year in Pondicherry. Well, I live in Pondicherry and can tell you that there are extreme periods when a fan is quite ineffective against a heady combination of an indoor ambient temperature above 30 deg.C and relative humidity above 90% (do you remember the terrible feeling after wiping your body after a cool shower to find yourself covered fully with sweat!). You are most welcome to visit our city but avoid these extremely sultry periods if you want to enjoy staying in the non-air conditioned heritage buildings that are so well designed to provide thermal and visual comfort during the remaining 4/5th of the year.

    Posted by: Anonymous | 7 years ago | Reply
  • Thanks Avikal I appreciate

    Thanks Avikal
    I appreciate your efforts in educating public how to use AC. I always run my AC at 26-28 degree cel and find that it is just right temp which our body requires. I don't find any logic in people running AC at 20 or 18 and then using blankets. Why should one become so unnatural. We have to pay a heavy price to nature for any mindless activity towards exploitation of any natural resource. Let sense prevail among us.

    Posted by: Anonymous | 7 years ago | Reply
  • The post is very good. Even I

    The post is very good. Even I prefer to set temperatures at 25-27. But I want to ask a question.
    My room is no 2nd floor & there is no further room constructed over my room. Isn't it running the ceiling fan might bring down the heat of ceiling to room & force AC to work harder to maintain the temperature?

    Posted by: Anonymous | 7 years ago | Reply
  • This is a good AC energy

    This is a good AC energy calculation system. It is a nice check. Keep it up!

    Posted by: Anonymous | 7 years ago | Reply
  • Dear Avikal The ceiling fan

    Dear Avikal

    The ceiling fan operating simultaneously with AC is again borrowed from west(mainly UK /USA) where they have insulated ceiling in order to save heating energy during winter are extreme going down to minus temperatures.In Indian condition operating a fan is more a psychological and it does not improve as when the fan is switched on only cold air will leak and the floor just outside room will sweat due to fresh air or warmer air gets mixed.

    Most of the splits or window air conditioner made or assembled are based on the conditions prevailing for majority of the western countries and where the split AC or window are predominantly used during the summer and for winter they have mostly heating requirement. To balance they set temperature at 18 to 20 C during winter to reduce heating energy and during summer they set at 22 to 24 C to reduce cooling energy.

    The split AC there is no provision of fresh air and windows used to have fresh air and has been discontinued almost by all countries as it was taking hot air and exhausting cold air, although some of the manufacturers claim they have the provision which is not effective.

    Posted by: Anonymous | 7 years ago | Reply
  • Avikal, Good initiative at


    Good initiative at right time,

    Thank you for taking your time and writing about the AC usage..

    It gave me a lot of information about handling and using AC and saving energy.

    Keep doing the good job... I also would like to compliment and appreciate other technocrats who participate in this discussion
    which is quite interesting.

    thank you once again .

    Sivakumar. Pillai

    Posted by: Anonymous | 6 years ago | Reply